Pressure regulator

ABSTRACT

A pressure regulator for use in regulating the outlet pressure of a pump for use in an engine comprises a piston member which is moveable with respect to an outlet opening under the influence of fluid pressure acting on the piston member to control the degree by which the outlet opening is obscured. The pressure regulator comprises a biasing arrangement for applying a biasing force to the piston member which opposes the pressure of fluid acting on the piston member. The biasing arrangement comprises a moveable abutment member which is cooperable with a stop member so as to vary the rate at which the displacement of the piston member varies with fluid pressure acting on the piston member. The stop member is pre-set in a fixed position relative to the regulator housing such that movement of the abutment member is terminated when the abutment member is urged into engagement with the stop member. The invention also relates to a transfer pump comprising a pressure regulator.

FIELD OF THE INVENTION

[0001] This invention relates to a pressure regulator suitable for usein regulating the outlet pressure of a low pressure, transfer pump of afuel system for a compression ignition internal combustion engine.

BACKGROUND OF THE INVENTION

[0002] It is known to use, as the transfer pump for use in a fuelsystem, a vane pump which is arranged to operate at a speed associatedwith engine speed. The vane pump may be provided with a regulator of thetype illustrated in FIG. 1, comprising a sleeve 10 within which a pistonmember 12 is slidable. The piston member 12 is biased by means of aspring 14 and is moveable under the action of the fuel pressure at theoutlet of the transfer pump. When the piston member 12 is in theposition shown in FIG. 1, the piston member 12 closes an outlet 16defined within the sleeve 10 to prevent fuel flowing through the outlet16 to the inlet side of the transfer pump. The piston member 12 ismoveable within the sleeve 10 to a position in which the outlet 16 isopen to allow fuel to return to the inlet side of the transfer pump.

[0003] The degree to which the outlet 16 is opened depends upon themagnitude of the pressure applied to the piston member 12. Byappropriate selection of the size of the piston member 12 and the spring14, the regulator can be set in such a manner that the outlet pressureof the transfer pump, as regulated by the pressure regulator, is relatedto the engine and pump speed in a desired manner.

[0004] The pressure at the outlet of the transfer pump, as modified bythe pressure regulator, is used to control various aspects of fuelsystem operation. For example, in some arrangements the pressure at theoutlet of the transfer pump, as modified by the pressure regulator, isused to adjust the maximum fuelling level of a high pressure fuel pumpwith which the transfer pump is associated. However, it has been foundthat setting of such transfer pumps is difficult as the relationshipbetween the outlet pressure and speed varies from pump to pump as aresult of production variations.

[0005] It is an object of the present invention to remove or alleviatethis problem.

[0006] By way of background to the present invention, CH 690 191 A5describes a pressure relief valve for relieving fluid pressure within aload chamber. The pressure relief valve is of the type having a valveneedle biased towards a valve seating by means of a spring load. Thevalve needle is caused to lift away from the valve seating in the eventthat fluid pressure within the load chamber exceeds a predeterminedamount, thereby opening communication between the load chamber and a lowpressure drain. The pressure relief valve also includes a piston whichis exposed to fluid pressure within a control chamber and which isengageable with a movable piece to alter the spring load acting on thevalve needle. By varying fluid pressure within the control chamber, thefluid pressure at which the valve needle is caused to lift from itsseating can be varied. The pressure relief valve is of the“plug-in-hole” type in which the valve needle extends into an opening inan insert which defines the valve seating. If fluid pressure within theload chamber is less than the predetermined relief pressure, thepressure relief valve is in a plugged position in which the valve needleextends into the opening and seats against the valve seating tocompletely close the opening, closing communication between the loadchamber and the low pressure drain. If fluid pressure within the loadchamber exceeds the predetermined relief pressure, the pressure reliefvalve is opened and the valve needle lifts off the valve seating torelieve pressure in the load chamber.

SUMMARY OF THE INVENTION AND ADVANTAGES

[0007] According to a first aspect of the present invention, there isprovided a pressure regulator for use in regulating the outlet pressureof a pump for use in an engine, the pressure regulator comprising apiston member which is moveable within a bore provided in a regulatorhousing with respect to an outlet opening under the influence of fluidpressure acting on the piston member to control the degree by which theoutlet opening is obscured, the pressure regulator comprising a biasingarrangement for applying a biasing force to the piston member whichopposes the pressure of fluid acting on the piston member, wherein thebiasing arrangement comprises a moveable abutment member which iscooperable with a stop member so as to terminate movement of theabutment member when the abutment member moves into engagement with thestop member, in use, thereby to vary the rate at which the displacementof the piston member varies with fluid pressure acting on the pistonmember, the stop member having a pre-set fixed position relative to theregulator housing.

[0008] Preferably, the biasing arrangement comprises a spring assemblycomprising first and second spring means.

[0009] Conveniently, the first and second spring means take the form offirst and second compression springs.

[0010] The regulator housing preferably takes the form of a sleeve. Itwill be appreciated that the regulator housing may include two or morehousing parts secured together, or may be a unitary part.

[0011] Preferably, the position of the stop member relative to theregulator housing is adjustable to permit adjustment of a pre-set fluidpressure at which the abutment member is caused to move into engagementwith the stop member.

[0012] When fluid pressure acting on the piston member exceeds thepre-set fluid pressure, the piston member is moved, against the biasingforce due to the biasing arrangement, through a sufficient distance tocause the abutment member to engage the stop member. During this stageof operation, the rate at which displacement of the piston member varieswith fluid pressure applied to the piston member is determined by thecharacteristics of both the first and second spring means. When themoveable abutment member moves into engagement with the stop membermovement of the abutment member is terminated, the second spring meansis disabled and the rate at which displacement of the piston membervaries with fluid pressure is altered. During this stage of operation,the rate at which displacement of the piston member varies with fluidpressure applied to the piston member is determined by thecharacteristic of only the first spring means.

[0013] The predetermined fluid pressure at which the moveable abutmentmember moves into engagement with the stop member can be adjusted byadjusting the position of the stop member relative to the regulatorhousing.

[0014] When the pressure regulator is used in regulating the outletpressure of a transfer pump for use in a fuel system, the speed of theassociated engine is related to the pressure of fuel acting on thepiston member. Hence, by adjusting the position of the stop member, theengine speed at which the moveable abutment member is caused to moveinto engagement with the stop member can be adjusted. The pressureregulator can therefore be adjusted to give the required transferpressure-engine speed characteristic.

[0015] The invention provides the advantage that, as the pressure-speedcharacteristic of the pump can be adjusted, pump to pump variations canbe compensated for. The pressure-speed characteristic of the pump canalso be selected so as to match the requirements of the particularengine.

[0016] Preferably, the stop member takes the form of an adjustmentscrew.

[0017] The pressure regulator preferably comprises an adjustment memberfor adjusting the pre-load of the biasing arrangement. Preferably, theadjustment member takes the form of a further adjustment screw.

[0018] Conveniently, at least a part of the stop member extends througha further bore provided in the adjustment member.

[0019] The moveable abutment member conveniently includes an annularregion defining first and second abutment surfaces, the abutment memberbeing arranged such that the first abutment surface is in abutment withone end of the first spring means and the second abutment surface is inabutment with one end of the second spring means.

[0020] Preferably, the piston member itself is arranged to obscure theoutlet opening, rather than any component carried by or otherwisecoupled to the piston member.

[0021] Preferably, the piston member shaped to cooperate with the outletopening so as to vary the extent to which the outlet opening isobscured, thereby to provide progressive opening of the outlet openingdepending upon the extent to which the piston member is displaced.

[0022] Preferably, the piston member is of generally cylindrical formand has a generally cylindrical outer surface which cooperates with theoutlet opening to vary the extent to which the outlet opening isobscured, depending on the position of the piston member within thebore.

[0023] The diameter of the piston member and the diameter of the boreare preferably selected to ensure movement of the piston member withinthe bore is guided.

[0024] In a preferred embodiment, the piston member is exposed to fuelpressure within an inlet chamber defined by the bore within which thepiston moves.

[0025] In a further preferred embodiment, the piston member is arrangedsuch that it can completely obscure the outlet opening to prevent fuelflow from the inlet chamber through the outlet opening.

[0026] The pressure regulator provides a continuous pressure regulatingfunction as the piston is urged to move against the spring load uponincreasing fuel pressure within the inlet chamber.

[0027] According to a second aspect of the present invention, a transferpump for use in supplying fuel to a high pressure pump for an enginecomprises a pump outlet through which fuel is supplied at a pressuredependent upon engine speed to the high pressure pump, the transfer pumpcomprising a pressure regulator as herein described which is arranged toregulate the pressure of fuel delivered by the transfer pump to the highpressure pump, in use.

[0028] In a preferred embodiment, the pressure regulator of the transferpump comprises an inlet region defined by the bore within which thepiston member of the pressure regulator moves to vary the extent towhich the outlet opening is obscured, the pump outlet being arranged todeliver fuel to the inlet region at a pressure dependent upon the enginespeed.

[0029] It will be appreciated that the second aspect of the inventionmay include any one or more of the preferred or optional features of thefirst aspect of the invention.

[0030] According to a further aspect of the present invention, a fuelsystem for supplying fuel to an engine comprises a transfer pump fordelivering fuel at relatively low, regulated pressure to a high pressurefuel pump, the high pressure fuel pump being arranged to deliver fuel tothe engine, wherein the fuel system comprises a pressure regulator asherein described which is arranged to regulate the pressure of fueldelivered by the transfer pump to the high pressure pump, in use.

[0031] It will be appreciated that the further aspect of the inventionmay include any one or more of the preferred or optional features of thefirst aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The invention will now be described, by way of example only, withreference to the accompanying drawings in which;

[0033]FIG. 1 is a sectional view illustrating part of a fuel pumpincluding a conventional pressure regulator;

[0034]FIG. 2 is a sectional view of a pressure regulator in accordancewith an embodiment of the present invention; and

[0035]FIG. 3 is a graph to illustrate pressure against engine speed forthe pressure regulator shown in FIG. 2 when employed in a fuel pump foruse in an engine.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0036]FIG. 2 illustrates a pressure regulator for use in regulating theoutlet pressure of a transfer pump 21 which is used to supply fuel to aninlet of a high pressure fuel pump (not shown) for supplying fuel to acommon rail or a distributed pumping system. The transfer pump 21 isarranged to draw fuel from a fuel reservoir 23 and supplies fuel at arelatively low pressure to the high pressure fuel pump.

[0037] The pressure regulator comprises a sleeve or regulator housing 20provided with a bore 22 within which a piston member 24 is moveable. Thepiston member 24 is of generally cylindrical form, the diameter of thepiston member 24 and the diameter of the bore 22 being selected toensure movement of the piston member 24 within the bore 22 is guided.The sleeve 20 is provided with an outlet opening 36 positioned suchthat, depending upon the position of the piston member 24 within thebore 22, the outlet opening 36 is either fully obscured by thecylindrical outer surface of the piston member 24, is partially obscuredby the outer surface of the piston member 24 or is fully open. Theoutlet opening 36 communicates with the fuel reservoir 23 so as toregulate the outlet pressure of the pump 21.

[0038] One end of the piston member 24 defines a surface 24 a which isexposed to fuel pressure at the outlet of the transfer pump 21 in aninlet region or inlet chamber 31 defined by the bore 22. The pressure offuel in the inlet region 31 determines the position of the piston member24 within the bore 22 and, hence, determines the rate of flow of fuelthrough the outlet opening 36. As fuel pressure within the inlet region31 increases, the piston member 24 gradually opens the outlet opening 36depending on fuel pressure within the inlet region 31, as described infurther detail below.

[0039] The pressure regulator also includes a spring assembly 25including first and second springs 26, 30, the spring assembly 25 beingarranged to apply a biasing force to the piston member 24 which opposesthe force due to fuel pressure acting on the piston member 24. Thespring assembly 25 also includes an abutment member 28 which is moveablewithin the bore 22 and is engageable with a first adjustment member 34in the form of a stop member upon movement of the abutment member 28beyond a predetermined amount, as will be described in further detailhereinafter. The moveable abutment member 28 includes an annular region28 a and is arranged between the first and second springs 26, 30 suchthat one end of the first spring 26 is in abutment with a first abutmentsurface defined by the annular region 28 a of the abutment member 28 andone end of the second spring 30 is in abutment with an opposing abutmentsurface defined by the annular region 28 a of the abutment member 28.The end of the second spring 30 remote from the abutment member 28 is inengagement with a further adjustment member 32 provided with a throughbore through which the stop 34 extends, the adjustment member 32 beingin screw threaded engagement with the sleeve 20 so as to permit theposition of the adjustment member 32 relative to the sleeve 20 to bevaried. It will be appreciated that the pre-load of the spring assembly25 can be adjusted by adjusting the position of the adjustment member 32relative to the sleeve 20. Typically, the stop 34 and the adjustmentmember 32 take the form of adjustment screws.

[0040] The abutment member 28 is provided with a first drilling 27 incommunication with a second drilling 29 provided in the stop 34. Theprovision of the drillings 27, 29 permits the region of the bore 22within which the first spring 26 is arranged to be vented, therebypreventing the piston member 24 becoming hydraulically locked within thesleeve 20. In addition, as a restricted flow of fuel is permittedthrough a relatively narrow clearance defined by the piston member 24and the bore 22, the provision of the drillings 27, 29 allows theeffects of viscosity on the operation of the pump to be compensated for(“viscosity compensation”). It will be appreciated that, although arelatively narrow clearance is defined between the piston member 24 andthe bore 22, the dimensions of the clearance are such that movement ofthe piston member 24 within the bore 22 is guided.

[0041] In use, prior to engine start up, the abutment member 28 occupiesa position in which it is spaced away from the surface 34 a of the stop34, the position of the adjustment member 32 relative to the sleeve 20being selected so as to provide the desired pre-load of the springassembly 25. Upon engine start up, as engine speed is increased, fuelpressure at the outlet of the transfer pump 21, and hence fuel pressurein the inlet region 31, is also increased, thereby causing the forceapplied to the surface 24 a of the piston member 24 to be increased.During this first stage of operation, a point will be reached at whichthe force due to fuel pressure acting on the surface 24 a of the pistonmember 24 is sufficient to overcome the biasing force of the springassembly 25 such that the piston member 24 is caused to move so as toopen, partially, the outlet opening 36. The outlet opening 36communicates with the fuel reservoir 23 such that fuel pressure at theoutlet of the pump 21 is regulated, depending on the extent to which theoutlet opening 36 is uncovered by the piston member 24. During thisstage of operation, the amount by which the piston member 24 isdisplaced as fuel pressure within the inlet region 31 increases will bedetermined by the spring characteristics of the first and second springs26, 30. As fuel pressure delivered to the inlet region 31 increases, theoutlet opening 36 will be opened progressively from a fully obscuredstate, in which the outer surface of the piston member 24 breakscommunication completely (except for minimal fuel leakage) between theinlet region 31 and the outlet opening 36, and a partially obscuredstate in which the outer surface of the piston member 24 partiallyobscures the outlet opening 36.

[0042] As engine speed increases further, fuel pressure at the outlet ofthe pump 21 continues to increase. When fuel pressure within the inletregion 31 exceeds a predetermined amount, the abutment member 28 isurged into engagement with the stop 34. Upon engagement between theabutment member 28 and the stop 34, movement of the abutment member 28is terminated and the second spring 30 becomes disabled such that, for afurther increase in fuel pressure within the inlet region 31, only thespring characteristic of the first spring 26 will determine the rate atwhich displacement of the piston member 24 varies with fuel pressure. Itwill therefore be appreciated that the rate at which displacement of thepiston member 24 varies with fuel pressure depends on whether theabutment member 28 is in engagement with the stop 34. Thus, at higherengine speeds, when fuel pressure at the outlet of the pump 21 isrelatively high, the pressure regulator has a different pressure-speedregulating characteristic compared with that at lower engine speeds.

[0043] During the second stage of operation when the second spring 30 isdisabled, the extent to which the outlet opening 36 is obscured willalso vary progressively with increasing fuel pressure within the inletregion 31 from a state in which the outlet opening 36 is partiallyobscured and a state in which the outlet opening 36 is opened to amaximum extent. It will therefore be appreciated that during both thefirst stage of operation, when both the first and second spring forcesact on the piston member 24, and the second stage of operation, whenonly the first spring force acts on the piston member 24, the extent towhich the outlet opening 36 is uncovered by the piston member 24 willvary progressively as fuel pressure in the inlet region 31 increases,even though the rate of displacement of the piston member 24 with fluidpressure will be different during the first and second stages. Thepressure regulator is configured such that, during both the first andsecond stages of operation, there is an approximately linearrelationship between the uncovered flow area presented by the outletopening 36 and fuel pressure in the inlet region 31.

[0044] In order to maintain control of pressure regulation, thecharacteristics of the first and second springs are preferably selectedto ensure that, when fuel pressure within the inlet region 31 reaches amaximum value for the particular pump/engine application and the outletopening 36 is opened to the maximum extent by the piston member 24 (i.e.the second stage of operation), the piston member 24 is in a position inwhich the outlet opening 36 is only partially obscured by the outersurface of the piston member 24.

[0045]FIG. 3 shows the relationship between the regulated pump outletpressure (i.e. in the inlet region 31) and engine speed. Upon enginestart up (engine speed A) to the point at which the engine reachesengine speed B, the force acting on the surface 24 a of the pistonmember 24 is insufficient to overcome the biasing force due to thespring assembly 25 such that the outlet opening 36 remains closed by thepiston member 24. Once the engine reaches engine speed B, the pressureof fuel at the outlet of the pump 21 is increased sufficiently to causethe piston member 24 to move within the bore 22 so as to compress thefirst and second springs 26, 28, movement of the piston member 24causing the outlet opening 36 to be partially opened, until the enginespeed increases to engine speed C. The rate at which the pump outletpressure increases with engine speed (i.e. the slope of thepressure-speed characteristic) between engine speeds B and C is governedby the spring characteristics of both the first and second springs 26,30.

[0046] Once the engine speed is increased beyond engine speed C, theforce due to fuel at the outlet of the pump acting on the surface 24 aof the piston member 24 is sufficient to cause the abutment member 28 tomove into engagement with the stop 34, thereby terminating movement ofthe abutment member 28 and disabling the second spring 30. For enginespeeds in excess of engine speed C, the relationship between pump outletpressure and engine speed is therefore governed only by the springcharacteristic of the first spring 26.

[0047] It will be appreciated that the engine speed C at which thesecond spring 30 becomes disabled, and hence the engine speed C at whichthe slope of the pressure-engine speed characteristic of the pump isaltered, is determined by the pre-set, fixed position of the stop 34within the bore 22. Thus, by adjusting the position of the stop 34relative to the bore 22 in the sleeve 20 prior to use of the pump, therequired fuel pressure at which the second spring 30 becomes disabledcan be pre-set to the desired value. The engine speed C at which thepressure-engine speed characteristic changes is therefore selected byadjusting the position of the stop 34 within the bore 22 prior to use ofthe pump.

[0048] The present invention provides the advantage that thepressure-engine speed characteristic of the pump can be adjusted byadjusting the position of the stop 34 and the adjustment member 32,thereby allowing pump to pump variations to be compensated for.

[0049] The invention also provides the advantage that thepressure-engine speed characteristic of the pump can be tailored so asto ensure the required transfer pressure is achieved at the two speeds(e.g. speeds D and E in FIG. 3) at which emission levels are measuredfor the purposes of regulatory approval. For a conventional pressureregulator, the rate of variation of transfer pressure with engine speedis substantially linear and so it is only possible to ensure the desiredtransfer pressure is achieved at one of the critical emissions speeds.

[0050] The present invention is also advantageous in that the adjustablepressure regulator occupies a relatively small volume of space.

What is claimed is:
 1. A pressure regulator for use in regulating theoutlet pressure of a pump for use in an engine, the pressure regulatorcomprising a piston member which is moveable within a bore provided in aregulator housing with respect to an outlet opening under the influenceof fluid pressure acting on the piston member to control the degree bywhich the outlet opening is obscured, and a biasing arrangement forapplying a biasing force to the piston member which opposes the pressureof fluid acting on the piston member, the biasing arrangement comprisinga moveable abutment member which is cooperable with a stop member so asto terminate movement of the abutment member when the abutment membermoves into engagement with the stop member, in use, thereby to vary therate at which the displacement of the piston member varies with fluidpressure acting on the piston member, the stop member having a pre-setfixed position relative to the regulator housing.
 2. The pressureregulator as claimed in claim 1, wherein the stop member takes the formof an adjustment screw.
 3. The pressure regulator as claimed in claim 1,wherein the biasing arrangement comprises first and second springmembers.
 4. The pressure regulator as claimed in claim 3, wherein thefirst and second spring members take the form of compression springs. 5.The pressure regulator as claimed in claim 4, wherein the moveableabutment member includes an annular region defining first and secondopposing abutment surfaces, the abutment member being arranged such thatone end of the first compression spring is in abutment with the firstabutment surface and one end of the second compression spring is inabutment with the second abutment surface.
 6. The pressure regulator asclaimed in claim 1, wherein the stop member takes the form of anadjustment screw.
 7. The pressure regulator as claimed in claim 1,further comprising an adjustment member for adjusting the pre-load ofthe biasing arrangement.
 8. The pressure regulator as claimed in claim7, wherein the adjustment member takes the form of a further adjustmentscrew having a position relative to the regulator housing which isadjustable prior to use of the regulator to adjust the pre-load of thebiasing arrangement.
 9. The pressure regulator as claimed in claim 7,wherein at least a part of the stop member extends through a boreprovided in the adjustment member.
 10. The pressure regulator as claimedin claim 1, wherein the outlet is provided in a side wall of theregulator housing.
 11. The pressure regulator as claimed in claim 1,wherein the piston member is shaped to cooperate with the outlet openingto progressively open the outlet opening depending upon the extent towhich the piston member is displaced.
 12. The pressure regulator asclaimed in claim 11, wherein the piston member is of generallycylindrical form and has a generally cylindrical outer surface whichcooperates with the outlet opening to progressively vary the extent towhich the outlet opening is obscured, depending on the position of thepiston member within the bore.
 13. The pressure regulator as claimed inclaim 12, wherein the diameter of the piston member and the diameter ofthe bore are selected to ensure movement of the piston member within thebore is guided.
 14. A transfer pump for use in supplying fuel to a highpressure pump for an engine, the transfer pump comprising a pump outletthrough which fuel is supplied at a pressure dependent upon engine speedto the high pressure pump, the transfer pump further comprising apressure regulator as claimed in claim 1 which is arranged to regulatethe pressure of fuel delivered by the transfer pump, in use.
 15. Thetransfer pump as claimed in claim 14, wherein the pressure regulator ofthe transfer pump comprises an inlet region defined by the bore withinwhich the piston member of the pressure regulator moves to vary theextent to which the outlet opening is obscured, the pump outlet beingarranged to deliver fuel to the inlet region at a pressure dependentupon the engine speed.
 16. A fuel system for supplying fuel to anengine, the fuel system comprising a transfer pump for delivering fuelat relatively low pressure to a high pressure fuel, the high pressurefuel pump being arranged to deliver fuel to the engine, the fuel systemfurther comprising a pressure regulator as claimed in claim 1 which isarranged to regulate the pressure of fuel delivered by the transfer pumpto the high pressure pump, in use.